An antenna array is a group of multiple active antennas coupled to a common source or load to produce a directive radiation pattern. Usually, the spatial relationship of the individual antennas also contributes to the directivity of the antenna array. A phased array antenna is an array of antennas in which the relative phases of the signals feeding the antennas are varied in a manner that the effective radiation pattern of the entire array is reinforced in a desired direction and suppressed in undesired directions.
FIG. 1 shows a diagram of a conventional antenna array 100. The antenna array 100 includes several linear arrays 104 housed in a (non-metallic) radom 102. Here, each linear array 104 is arranged vertically with spacing between each other, which is determined by the desired resonant frequency of the antenna array 100. Each linear array 104 is connected to its associated radio frequency (RF) electronics circuitry contained in an external RF electronics module 108, via an antenna feed 106. The RF electronics module 108 is connected to external systems via a connection 110 for power, control, and communications connections; and may be physically mounted on the radom 102, or may be located remotely or outside of the antenna array 100.
An Electronically Scanned Array (ESA) is a type of phased array antenna, in which transceivers include a large number of solid-state transmit/receive modules. In ESAs, an electromagnetic beam is emitted by broadcasting radio frequency energy that interferes constructively at certain angles in front of the antenna. An active electronically scanned array (AESA) is a type of phased array radar whose transmitter and receiver (transceiver) functions are composed of numerous small solid-state transmit/receive modules (TRMs). AESA radars aim their beam by emitting separate radio waves from each module that interfere constructively at certain angles in front of the antenna.
Digital beamforming is a signal processing technique used in sensor or radar arrays for directional signal transmission or reception. Digital beamforming is attained by combining elements in a phased array in such a way that signals at particular angles experience constructive interference, while other signals experience destructive interference. Digital beamforming can be used at both the transmitting and receiving ends in order to achieve spatial selectivity. An advantage of digital beamforming is transmitting multiple simultaneous summed signals through each radar element.
Modern radar, radar jammer and communications antenna systems often require wideband frequency capability within constrained volume allocations. Electronically Scanned Array (ESA) antenna and Active Electronically Scanned Array (AESA) antenna designs provide dense-packed, high-reliability electronics. Moreover, there are growing interests to use digital beamforming to transmit two different types of signals simultaneously such as communications (comms) and radar, comms and electronic warfare (EW), or EW and radar. This requires spectrum sharing, that is, the two different types of signals, for example, an RF signal for military or radar applications, and a lower frequency (communication) signal for command and control applications, need to be simultaneously transmitted off a radar array.
Conventionally, these two types of signals are modulated into a single signal and the single modulated signal is amplified before it is transmitted by the radar array. However, the RF signal normally requires high power amplification, which is generally achieved by a high power amplifier (HPA) operating in its saturated region, while the lower frequency signal requires a lower amplification and needs the amplifier to operate in its linear region, not to miss any information from the signal.
The present invention enables an antenna array or any other transmitter to simultaneously transmit two or more combined signals out of the same antenna element with different power amplification levels for each signal to efficiently amplify a multi-carrier signal.